The invention relates to an electric motor with an electromagnetically actuated brake.
From the German patent DE 41 26 672 C2 an electric motor with an electromagnetically actuated brake is known. The brake comprises between a body of an electromagnet and a brake disk an axially movable armature plate that is guided nonrotatably along a shaft of the electric motor. The shaft is supported by a brake-mounting end shield of the motor, which closes off the end of a housing of the motor. The shaft extends through the brake-mounting end shield to the exterior thereof. When the brake is applied, i.e. after the current through the electromagnet has been turned off, the armature plate is pressed by spring force against brake linings of a lining carrier that is connected to the shaft on the outside of the brake-mounting end shield. The armature plate thus stops the rotational movement of the lining carrier by friction against the brake lining, as soon as the magnetic field of the electromagnet has sufficiently decayed.
When the brake is being raised, i.e. in particular when the current through the electromagnet is turned on, a force is exerted on the armature plate, in particular an attractive magnetic force, which is stronger than the opposing mechanical force exerted by the springs, so that the armature plate is released from the lining carrier and returns to rest against the magnet body.
The armature plate is guided in such a way that it cannot rotate about the axis of rotation of the shaft, which in the known electric motor is achieved by axial bores or axially directed recesses in the armature plate, through which extend in the axial direction bolts or screws that simultaneously attach the magnet body of the brake to the brake-mounting end shield of the electric motor.
These bolts or screws also determine the distance in the axial direction between the brake-mounting end shield of the motor and the magnet body of the brake, so that an axial travel distance for the operation of the brake, or the axial movement of the armature plate, is specified. By adjusting the bolts or screws, the axial travel can be reduced, in order to compensate for frictional wear of the brake lining on the carrier disk.
An electric motor with brake of the kind described in DE 41 26 672 C2 is also known to comprise a terminal box for electrically connecting the motor and the brake. From the terminal box, cables to supply the brake or its electronics pass to the brake through the end of the housing on the brake side of the electric motor.
The brake described in DE 41 26 672 C2 is a pre-fitted brake, which is mounted directly as part of the electric motor. Therefore the brake can be made compact. The overall length, the weight and the work of manufacturing it are thus less than in brakes constructed separately which need to be installed subsequently on the housing of the motor.
One such subsequently installed brake, for example, is screwed to a flange on the outer surface of an end face of the electric motor. In order to bear the weight of the brake, the flange is of relatively thick and stable construction. The outer side of the flange serves as brake surface, against which the lining carrier rotating with the shaft is pressed when the brake is applied. The lining carrier, as in the case of the pre-fitted brake described above, comprises on its side facing away from this frictional flange surface a brake lining which, when the brake is applied, performs frictional work on the armature plate. The armature plate of the subsequently installed brake likewise is secured against rotating with the motor shaft by bolts or screws, which simultaneously serve to attach the electromagnet to the flange.
During installation or maintenance of known electric motors with electromagnetically actuated brakes, in many cases the brake can be installed or removed only together with the brake-mounting end shield of the motor. In other cases, although the brake can be taken away from the end shield while leaving the latter attached to the motor, there are other parts besides the lining carrier between the shield of the brake and the brake-mounting end shield of the motor, which must be installed individually or which when the brake is being removed can unintentionally become detached and fall down. Examples of such additional parts include compression springs, which press a brake inductor core by way of pressure rings aginst the stop provided by long fixation screws, and spacer sleeves to determine the axial distance between brake shield and motor end shield.
Furthermore, when the braking process is initiated, i.e. when the brake is applied, in the electric motors with brakes described above the armature plate and/or the fixation bolts or screws or the spacer sleeves are exposed to wear and tear because owing to its braking torque the armature plate strikes against the bolts or screws. The parts thus striking against one another are customarily all made of metal, which causes a high degree of wear. The noise produced by these impacts is also frequently disturbing. In some conditions, it is impossible to maintain the prescribed noise limits in the workplace. In addition, the effort of installing and removing many individual parts and the costs of manufacturing them are considerable.
When brakes are being removed from an electric motor into which one or more cables pass, if the work is not carried out with the greatest care and precaution, the cables may be damaged or even torn out.
It is the object of the present invention to disclose an electric motor with an electromagnetically actuated brake of the kind cited above that is reliable in operation and in which the effort of installing and removing the brake is minimized.
In accordance with the invention the brake is constructed as a completely prefabricated unit which can be screwed to the housing of the electric motor.
The brake rotor, however, is already provided within the completely prefabricated brake, so that the entire component represented by the prefabricated brake can be installed on the electric motor by inserting the shaft of the motor into the brake rotor, after which all that must be done is to create the mechanical connection (fixation bolts) between brake and motor.
Therefore when the brake is being installed, all that is required is to connect the brake rotor in a rotationally stable manner to the shaft of the electric motor and fix the brake to the housing, in particular by means of screws. The installation of other individual parts such as spacer sleeves, compression springs and the like is eliminated. Therefore operations, in particular exchanging the brake for a replacement, can be carried out in an extremely short time. This is especially important for use in mass-production equipment, because the stoppage time for maintenance can be kept short. Furthermore, the brake-mounting end shield of the electric motor need not be removed, so that during the maintenance work the interior of the motor remains largely protected from dirt. Complete prefabrication also offers the advantage that the brake can be more rapidly and hence economically assembled at the site of manufacture than at the place where it is to be used.
When such a prefabricated brake in accordance with the present invention is compared with a conventional, completely assembled brake for subsequent installation, the main difference is that once the assembly of a brake according to the state of the art has been completed, the brake is functional in itself, whereas the prefabricated brake disclosed here initially does not function. The reason is that it lacks the brake-mounting end shield of the electric motor, without which neither the large moment of torque produced here nor the heat generated during braking can be dissipated.
Preferably a plug-and-socket device is provided through which current can be supplied to the coil of the brake""s electromagnet, which can be connected together when the brake is being installed, in particular is being screwed onto the housing of the electric motor. This measure allows the cable connections between the motor and the brake to be free of imposed loads and therefore to remain undamaged even though no particular care is taken. Installation is additionally simplified in that the electrical connections need not be produced by screwing cables on. In particular with suitable integration of the plug-and-socket device into the housing of the motor and/or into the brake, the electrical connection is produced simply by setting the brake onto the housing.
Especially preferred is a further development in which the guide mechanism, by means of which the armature plate is made substantially nonrotatable but can be displaced axially in the direction of the shaft of the electric motor, is constructed as a ring connected, in particular screwed, to the magnet body. The ring can in particular be made of a plastic material by injection molding. In any case, however, the ring serves several functions, namely a housing function and the guide function for the armature plate, so that a high degree of integration and modularity is achieved. As opposed to several bolts or screws, which take over the guide function in known electric motors, the ring has the advantage of being a single component or component group, which can be more simply and cost-effectively installed.
Preferably the ring establishes a distance in the axial direction between the brake-mounting end shield and the magnet body of the brake, so that a fixed, nonadjustable axial travel distance is specified for actuation of the brake. In this case, brake linings or in particular a brake lining with high resistance to abrasion is used, so that replacement is necessary only after many braking cycles. In this further development, the ring also serves to establish the distance between the brake end shield of the electric motor and the magnetic body of the brake. Therefore the technically elaborate maintenance procedure of adjusting the distance is eliminated. By dimensioning the ring precisely, the distance can be determined once and for all in advance, during manufacture. In order to employ distances that differ slightly from one another, a useful solution is to manufacture a plurality of different rings and keep them in reserve for use as needed. By this means, in the rare cases in which adjustment of the axial travel is required in order to operate the brake, it can be achieved by simply exchanging the ring. It is also possible in this way to change the distance when a brake is to be used for different purposes. Preferably the ring is screwed to the brake shield with only short screws (in comparison to the long screws used to attach the brake to the motor). Hence the ring can be exchanged in an extremely short time.
Preferably the ring comprises at least one groovelike, axially extending guide recess to accommodate a projection from the armature plate. Alternatively, the ring can bear the projection and the recess can be formed on the armature plate. In either case reliable guidance is produced, which prevents the armature plate from rotating with the shaft of the electric motor during braking. In particular if the ring is made of plastic, during braking the impact- and noise-attenuating properties of plastics are advantageous. The amount of wear is slight.
In a favorable embodiment of the brake in accordance with the invention the guide mechanism and the magnet body comprise sealing devices to seal the prefabricated brake. For example, by circumferential sealing rings inserted into grooves in the shield the movable parts of the brake can effectively be protected from the entry of dirt. This contributes to lowering the frequency of maintenance.
Preferably the ring comprises first parts of a pin-and-socket device and the brake-mounting end shield comprises second parts thereof, which serve to conduct current to the brake coil and/or to electronic circuitry associated with the brake. The first and second parts of this device are so constructed that when the brake is being screwed onto the housing, they come into electrical contact with one another. In particular, the first parts of the pin-and-socket device are integrated into the ring in such a way that they can be connected to the second parts during installation without exact positioning of the brake, the pin-and-socket device itself guiding the brake into just the right mounting position. Subsequently the brake need merely be screwed onto the housing of the electric motor.
It is advantageous for the brake rotor and also the armature plate to be disposed so that they can be axially displaced. A drive element connected to the shaft is preferably provided to carry the brake rotor along in a rotationally stable manner.
Preferably during the braking procedure the brake rotor comes into engagement with a metal friction sheet disposed on the brake-mounting end shield, where it performs braking work when no current is supplied to the brake coil.
An important aspect of the present invention lies in the fact that the prefabricated brake in accordance with the invention in itself can be manipulated as a single component; that is, it is unlike the brakes known according to the state of the art in that the latter must be installed piece by piece on an electric motor, thus acquiring their final form only gradually, in successive increments. This cohesiveness of the various components in the present invention is achieved by a friction sheet which, so to speak, is positioned as the outermost component or final component between the brake housing and the brake-mounting end shield of the electric motor, and which is fastened to the housing parts of the prefabricated brake. As a result of this friction sheet the brake is closed on the side facing the electric motor (during installation), apart from an opening through which the shaft of the motor passes, so that all the brake components are held together. In the installed state, i.e. when the prefabricated brake has been installed on an electric motor, the friction sheet is in direct contact with the brake-mounting end shield of the electric motor, so that the torque produced during braking and the heat generated in the process are taken up by the brake-mounting shield of the electric motor.
In a particularly advantageous embodiment the brake rotor comprises a brake body that extends in one continuous piece in the axial direction, in order to generate braking friction on the armature plate and where appropriate also on the brake-mounting end shield or on the friction plate. In particular when a long-lived material is used for the brake rotor and when a ring is used as guide mechanism for the armature plate, in this way later adjustment of the brake can be avoided.
As opposed to known embodiments of brake rotors, in which a lining carrier bears separate brake linings on one or both sides, because the above measure involves fewer different parts it allows smaller dimensional tolerances to be maintained during manufacture, so that it is possible to achieve the target value for the axial travel distance in operation of the brake without subsequent reworking.
Embodiments of the brake rotor are also known in which the braking surface on the end face of the brake rotor to generate braking friction on the armature plate and where appropriate on the brake-mounting end shield is interrupted or covered with several separate brake linings. In a further development the brake rotor advantageously has on its end face a substantially rotationally symmetrical braking surface to generate braking friction on the armture plate and where appropriate a second such braking surface to generate braking friction on the brake-mounting end shield or on the friction sheet. Hence the braking surfaces can be enlarged as compared to known constructions, which tends to prolong the operating life of the brake linings or the in particular one-piece brake rotor.